During the next year of the research grant period (1978/79) we will study the toxicity of two new intravascular silicone rubber formulations developed during the previous year (1977/78): 1. extremely low viscosity silicone rubber (16 centistokes) with a new crosslinking chemistry; and 2. a silicone rubber foam. We will investigate the effect of the two new silicone formulations on the blood elements, particularly hemolysis. Preliminary information indicates that the low viscosity silicones produce hemolysis. Histological sections of the injected material in the peripheral artery of a rabbit or a rat using standard light microscopy and the scanning electron microscope will be reviewed to look for any damaging effect of the injected material on the vascular wall and to study the manner in which the substance adheres to the intima. The scanning electron microscope is ideally suited to this purpose. Preliminary results are very interesting. We will also carry out an evaluation of a new method of injecting the intravascular adhesive - isobutyl-2-cyanoacrylate. The proposed method is intended to decrease the risk of catheter adhesion to the vessel wall.